1. Field of the Invention
The invention pertains to the field of shock protection circuits in general and in particular to immersion detection current interrupter circuits designed to protect the user of a small hand-held electrical appliance from a serious electrical shock if the appliance is immersed in or otherwise comes into contact with an electrically conductive fluid.
2. Description of the Prior Art
Shock protective circuits known in the prior art are of two types, ground fault current interrupter circuits (GFCI) and immersion detection current interrupter circuits. Various devices incorporating such circuits are also known in the prior art. GFCI devices are presently required in new electrical installations in bathrooms and other locations. Typically, such devices are included in an assembly connected to an electrical outlet.
Prior art shock protection circuits are designed primarily for electrical devices of substantial size and cost. They tend to be sophisticated, complex devices which, while of substantial economic and safety value, are not appropriate for the volume and variety of inexpensive consumer products in the field of hand-held small electrical appliances. Typical of the prior patent art are the ground fault current interrupting devices disclosed in U.S. Pat. Nos. 4,345,289 and 4,358,708 for use in residential applications. A typical industrial hazard protection device is disclosed in U.S. Pat. No. 4,103,319. Such devices are inappropriate in terms of size, complexity and cost for small consumer appliances.
Shock protection is presently required for wall-mounted hair dryers under UL 859, which is presently a limited standard of dubious value. The closest specific prior art patent is U.S. Pat. No. 4,493,975 which discloses a wall-mounted hand-held hair dryer. The principal power switch for the appliance is contained in the wall-mounted housing. When the appliance is removed from the wall mount, this switch is in the "off" position and no power flows to the appliance. Thus, if the appliance should accidentally or intentionally be immersed in a conductive fluid, it is electrically dead and no shock hazard is present. It thus satisfies the present UL standard 859. To turn on power to the appliance, the user must activate a switch in the wall mount. Simply returning the hand held dryer to the wall mount turns the switch off. The problem with this prior art device and the UL standard itself is that there is no protection from electrical shock when the power switch is in the "on" position.
However, simple, reliable, inexpensive shock protection circuits incorporated in components small enough to be used in hand-held personal care appliances such as hair dryers and curling irons, and similar consumer appliances and tools are not disclosed in the prior patent art nor are such devices commercially available.
The prior art fails to disclose a simple, inexpensive circuit embodied in a small component device which serves to protect the user of a small electrical appliance from electrical shock if the appliance comes into contact with an electrically conductive fluid such as water. The most frequent hazard of this type is the use of hair dryers in a bathroom. When a personal care appliance such as a hair dryer or electric razor come into contact with water, the user may receive an electrical shock which can be fatal. The object of the present invention is to protect the user from a serious shock (above 0.005 amps) while meeting, or exceeding, the requirements of UL 859, paragraph 28.1, and equivalent standards either now in force or to be in force in the near future.